Neurogenesis occurs in the dentate gyrus (DG) of the hippocampal formation (HF) of adult mammals and is altered in both health (aging) and disease (stress, neurological damage) states. Decreased neurogenesis is an emerging model for the etiology of major depressive disorder (MDD). Antidepressant treatment (ADT) increases neurogenesis in the DG of rodents. Therefore, restoration of neurogenesis may be an antidepressant therapeutic effect. However, this has yet to be examined in the human brain. Studies will be carried out in three groups: 1. Patients with Mood Disorder (MD, n=20) who were on antidepressants (ten treated with selective serotonin reuptake inhibitors, SSRI, ten treated with tricyclic antidepressants, TCA) or lithium (n=6) at the time of death; 2. MD patients (n=20) who were not on antidepressants for e 3 months and 3. normal, non-psychiatric controls (n=18). The three groups will be matched for sex, age (range 24 to 62 years in the whole sample), postmortem interval (PMI), suicide and race. We will also match the MD groups on proportions with comorbid diagnoses and the percentage that have MDD or bipolar disorder. All cases, including controls, will have psychological autopsies determining DSM Axis I and Axis II diagnosis, as well as neuropathologic examination and brain toxicological screen. Immunocytochemistry for Ki67, a cell cycle protein expressed during mitosis, will be used to identify dividing cells. Double labeling with antibodies for multipotent progenitor cells (Nestin, Pax6, GFAP), neuronal progenitors cells and neuroblasts (TUC-4, TUJ-1, PSA-NCAM), or immature glia (Vimentin) will be used to establish the phenotype of the dividing cells. The HC from MDD patients with and without SSRI, TCA or lithium and controls will be assayed. Stereology will be used to estimate the labeled cell number in the DG of the HF. The number of dividing cells (Ki67-immunoreactive [IR]), multipotent progenitors (TUC-4), and neural progenitor/neuroblasts (TUC-4-IR) will be examined along the antero-posterior axis of the hippocampus, and compared across the lifespan, between MD and normal controls and between MD patients without treatment and MD subjects who were on SSRI, TCA or lithium. The rostrocaudal extent of the right dentate gyrus will be used for the study and series of sections at 2mm intervals will be assayed for each antibody. We will test the hypotheses that neurogenesis: 1. is more pronounced in the anterior versus posterior HC; 2. is decreased in MD versus controls, and 3. MD patients receiving SSRI or TCA may have more Ki67- IR and Nestin-IR cells compared to MDD patients without treatment; on the other way we hypothesize fewer TUC-4-IR cells in antidepressants treated versus untreated cases. In an exploratory analysis we test the same effects for or lithium. These results have implications for understanding the pathophysiology of depression and the mode of action of antidepressants and lithium treatment.